Front projection photographic apparatus conventionally comprises a projector for projecting onto a screen a background image, so that a subject can be photographed against the projected image by a camera located on the same side of the screen as the projector. The screen should have high reflectivity along the projection axis of the apparatus, so that the projected light reflected from the subject is of low intensity compared with that reflected from the screen. The shadow on the screen formed by the subject in the light from the projector must not of course appear in the photograph, so a semi-reflective or half-silvered mirror is used to enable the camera to see the projected image along the projection axis. It is necessary also that the nodal points of the lens system of the projector and the camera be coincident.
Front projection apparatus has accordingly been constructed in the past as a support structure for mounting the projector so as to throw its beam for example substantially vertically upward onto a half-silvered mirror arranged to reflect the beam substantially horizontally. The structure also receives the camera in a position to view the projected image through the mirror along the axis of the projected beam. The support structure conveniently holds the projector and the mirror in fixed relation and provides a camera mount adjustable for a variety of cameras.
To effect the precise adjustment of the camera position necessary for the best results, light is projected outwardly through the camera lens system, only a very narrow beam being projected, as by restriction of the iris, for example, a very narrow beam is projected also through the projector. The camera position is adjusted until these two beams are seen to be aligned at any position along the projection axis. The camera body can then be clamped to the apparatus. This procedure is laborious and time-consuming and discourages use of the apparatus.
It is essential for best results not only that the camera views along the projection axis, but also that the nodal points of the camera and projector lens systems be coincident on the axis. If this is not so and the camera is in effect rearward of the projection position a fringe will be noted on the resultant photograph at the edges of the subject. If the camera is in effect forward of the projection position, a fringe will be noted similarly at any internal edge of the subject. This disadvantage can readily arise in practice, because any movement of the subject after the apparatus has been set up which requires refocussing of the camera, will displace the camera nodal point with respect to that of the projector.
It is among the objects of the invention to provide a sighting or registration means whereby a camera can be correctly positioned with respect to a front projection apparatus in a simple way.
It is a further object of the invention to provide for the correct positioning of a camera in relation to a front projection apparatus without the need for optical adjustment.
It is another object of the invention to provide means for reception of a camera on a front projection apparatus so as to permit adjustment of the camera focus without need for movement of the camera as a whole.
It is yet another object of the invention to provide means for securing the lens system of a camera in a predetermined axial and/or lateral positional relationship to the projection axis of a front projection apparatus.